The present invention relates in general to sewing machines and in particular to a new and useful upper cloth feed for a sewing machine which has adjustable tensioning means for applying a variable degree of tension to an upper cloth feed foot and a cloth pressure foot.
Upper cloth feeds for sewing machines are known which include a pressure foot and an upper feed foot which is connected over rods to a feeding and lifting drive. In such an upper feed device (as shown in German OS No. 20 57 450), one compression spring acts on the feed foot and another acts on the driving connection between the upper feed foot and the presser foot. Due to the idle stroke existing between the lifting drive and the presser foot, the presser foot remains likewise on the sewing material during the advance phase of the sewing material in which the upper feed foot bears on the sewing material. In the resting phase of the sewing material, the upper feed foot is lifted from the sewing material by the lifting drive.
Due to this procedure, both compression springs stress the presser foot in the resting phase of the sewing material, while in the moving phase one compression spring stresses the upper feed foot, and the other compression spring stresses the presser foot.
The known arrangement has the disadvantage that a desired distribution of the pressure forces on the upper feed foot and the presser foot, as is required for the proper sewing of different materials, is very cumbersome and can only be achieved by several readjustments of the two compression springs.
Even when replacing the existing upper feed foot by one with a different working range, such a readjustment of the pressure forces on the two sewing feet is necessary. Upper feed feet with soles that work ahead or in the range of the needle are suitable for differential sewing operations, while for sewing material layers of equal length, upper feed feet with soles that work behind the needle are provided. When replacing such feet with a different working range, the pressure distribution therefore changes likewise, and must be readjusted. If this readjustment is very elaborate, an exact material adjustment is frequently foregone or is only made incompletely, and the result shows corresponding drawbacks.